I bought a "vintage" Auto-Tune engine analyzer with an inductive pickup to help diagnose a rough idle issue. Engine is running rough and shaking pretty badly below 1500 rpm.
I'm finding that the rpm on the Auto-Tune does not agree with the mechanical tach and becomes very unstable below about 1500 rpm, which correlates well with where the engine is also running poorly. The analyzer shows a higher rpm than the engine is actually running, sometimes as much as double. The behavior varies depending on which cylinder I clip the pickup on. Some are worse than others.
Anybody have any insight as to what is going on here? I have never use one of these engine analyzers before.
For reference, here's what I have done to work on this issue. The shaking made me think it was timing related, so I started there. Normally I don't like to just throw parts at a problem, but looking at my records, many of them were very old and probably due.
- verify correct operation of both mechanical and vacuum advance (distributor was rebuilt by Jeff at Advanced about 5 years ago)
- reset static timing to zero, then dial to 4 deg advance. Driving test resulted in going to 12 deg advance which is where I am now.
- replace points (they were pitted), cap, rotor (broken and loose on the shaft), cap, plugs, wires
- new Pertronix coil (old one did test OK though)
I'm planning to tune and balance the carbs next. They have relatively few miles on a rebuild and should be in good shape.
Thanks!
I'm finding that the rpm on the Auto-Tune does not agree with the mechanical tach and becomes very unstable below about 1500 rpm, which correlates well with where the engine is also running poorly. The analyzer shows a higher rpm than the engine is actually running, sometimes as much as double. The behavior varies depending on which cylinder I clip the pickup on. Some are worse than others.
Anybody have any insight as to what is going on here? I have never use one of these engine analyzers before.
For reference, here's what I have done to work on this issue. The shaking made me think it was timing related, so I started there. Normally I don't like to just throw parts at a problem, but looking at my records, many of them were very old and probably due.
- verify correct operation of both mechanical and vacuum advance (distributor was rebuilt by Jeff at Advanced about 5 years ago)
- reset static timing to zero, then dial to 4 deg advance. Driving test resulted in going to 12 deg advance which is where I am now.
- replace points (they were pitted), cap, rotor (broken and loose on the shaft), cap, plugs, wires
- new Pertronix coil (old one did test OK though)
I'm planning to tune and balance the carbs next. They have relatively few miles on a rebuild and should be in good shape.
Thanks!